This application claims the priority of German patent 197 14 937.5, filed Apr. 10, 1997, the disclosure of which is expressly incorporated by reference herein.
This invention relates to a data bus system for motor vehicles.
Data bus systems for data communication of this type are, for example, known from the controller area network (CAN), in particular from control devices in motor vehicles. The concept of communicating data in motor vehicles with the aid of a CAN, the function of the CAN, as well as a possible architecture of a CAN-module, are, for example, known from the BOSCH brochures "The Optimized Bus System for a Serial Data Transmission in Motor Vehicles," and also from "Functional Description," and "Architecture of the CAN-module AN 82526," dating from the year 1987. This known data bus system is constructed in a linear fashion. A number of electronic bus stations, in particular control devices of a motor vehicle, are connected to a data bus. In addition to the connection to the data bus, these bus stations can exhibit an additional input or output port to, for example, connect sensors and actuators or to connect to the power supply. This known data bus system operates in accordance with the multi-master principle, i.e., all bus stations have equal access. When the data bus is free, each bus stations can begin to transmit its data telegram. The telegram of a transmitting bus station is received by all bus stations and confirmed, but only analyzed by the bus stations that require the data of these telegrams.
However, other data bus systems of motor vehicles are known. Normally the bus stations of a data bus system of motor vehicles exhibit a power supply that is either turned off when the ignition is turned off and is only turned on by turning the ignition on (power supply via the so-called "binding post 15"), or one that exhibits a bus station power supply port which is inseparably connected to the motor vehicle battery, even when the ignition is turned off (Power supply over the so-called "binding post 30"). In the power supply system in accordance with the first alternative, data exchange between the bus stations, which could be required in certain situations, is not possible when the ignition is turned off, while the power supply system in accordance with the second alternative results in an undesirably high quiescent current usage.
A goal of the present invention is to create a data bus system in which the quiescent current is reduced to a minimum when the ignition is turned off, while still enabling necessary functions.
This and other goals have been achieved according to the present invention by providing a data bus system for a motor vehicle, comprising a plurality of electronic bus stations, each of said bus stations having an input port that is connected a battery of the motor vehicle to supply power to the bus stations, wherein each of said bus stations is equipped with a detector circuit and a controllable switch that turn off the supply of power to the bus station in a ground state when an ignition of the motor vehicle is turned off, with the exception of the detector circuit, by opening the switch, wherein during a temporarily required data exchange between selected ones of the bus stations, the controllable switch of each of said selected bus stations is closed by its detector circuit during a selective wake state, and wherein at least one of the bus stations is selected as a main bus station to control said wake state.
This and other goals have been achieved according to the present invention by providing a data bus system for a motor vehicle, comprising: a power supply which supplies power when an ignition of the motor vehicle is turned off, a plurality of electronic bus stations connected with each other via a data bus, each of the bus stations having a controllable switch which selectively connects the bus station to the power supply and disconnects the bus station from the power supply, each of said bus stations having a detector circuit connected to the power supply independently of the controllable switch, wherein when the ignition of the motor vehicle is turned off, the controllable switches disconnect the bus stations from the power supply until the detector circuits recognize that a data exchange is required between selected ones of the bus stations, at which time said detector circuits of said selected ones of the bus stations send a signal to said controllable switches of said selected ones of the bus stations to connect said selected ones of the bus stations to the power supply until said data exchange is completed, after which the controllable switches disconnect said selected ones of the bus stations from the power supply.
This and other goals have been achieved according to the present invention by providing a method of exchanging data in a data bus system for a motor vehicle, said method comprising the steps of: providing a power supply which supplies power when an ignition of the motor vehicle is turned off, connecting a plurality of electronic bus stations with each other via a data bus, providing each of the bus stations with a controllable switch which selectively connects each of the bus stations to the power supply and disconnects the bus station from the power supply, providing each of said bus stations with a detector circuit connected to the power supply independently of the controllable switch, wherein when the ignition of the motor vehicle is turned off, the controllable switches disconnect the bus stations from the power supply until the detector circuits recognize that a data exchange is required between selected ones of the bus stations, at which time said detector circuits of said selected ones of the bus stations send a signal to said controllable switches of said selected ones of the bus stations to connect said selected ones of the bus stations to the power supply until said data exchange is completed, after which the controllable switches disconnect said selected ones of the bus stations from the power supply.
The fundamental idea of the invention lies in the creation of a selective wake state when the ignition is turned off, enabling an intermittent data exchange between selected bus stations that are each assigned to certain necessary functions. In accordance with the invention, the bus stations are therefore normally disconnected from the power supply when the ignition is turned off (i.e., bus stations are in a sleep state) and are only briefly turned on or supplied with voltage during the temporarily required data exchange between selected bus stations (i.e., bus stations are in a wake state). For this, at least one bus station is defined as the main bus station in order to control the respective wake state, although in principle the bus stations can have equal access. In order to realize the selective wake state, the bus stations have to exhibit an added feature in the form of a detector circuit that is supplied with current, even when the bus station is turned off. However, since only the detector circuits have to be supplied with current, the quiescent current usage is reduced to a minimum since the power supply is always turned off from the bus stations. The detector circuit can thereby be integrated into the hardware of the bus station or be connected externally to the bus station. The detector circuit of a main bus station can furthermore differ from the detector circuits of the remaining bus stations. In addition, all bus stations can be main bus stations in the sense that they can control a selective wake state. A main bus station can either be awakened by an external wake input (interrupt input) or can wake itself, for example, by a real time clock connected to the detector circuit.
As a further development of the invention, the main bus station exhibits a circuit that sends a selection telegram to the data bus by which each temporarily required data exchange between selected bus stations can be determined in order to activate a necessary data exchange. In a storage device of the main bus station, for example its microprocessor or in its detector circuit, information is stored as to when and, if needed, how long a data exchange is necessary, and which bus stations are to be selected for each necessary data exchange. The main bus station can therefore also be a selected bus station.
In another advantageous embodiment of the present invention, the detector circuits of all bus stations receive the selection telegram in order to determine whether the bus station assigned to them is selected, and only when this occurs turn the power supply on. The process of turning the power off occurs, for example, in the main bus station, in particular by turning off all bus telegrams or by issuing a dominant bus signal, for example by over-writing an existing transmission with a long high level. In known bus systems (CAN, for example) the bus stations recognize that it usually deals with a bus protocol violation in the second variation, upon which they terminate their transmission.
In addition, not only detector circuits, but also the controllable switches for turning the power supply on and off may either be integrated in the respective bus stations or may be externally connected to the respective bus stations. The connection to the controllable switch in the detector circuit exterior of the bus stations has the advantage that data bus systems already available can be upgraded without changing the bus stations. However, in principle an integration of the detector circuit and the controllable switch into the bus stations housing is preferred.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.